Author

Chung Nga Ko

Year of Award

4-28-2020

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Chemistry

Principal Supervisor

Ma, Edmond Dik Lung

Keywords

Iridium ; Transition metal complexes ; Luminescent probes

Language

English

Abstract

Transition metal complex, especially iridium(III) complex, possesses substantial advantages in sensing applications. To date, a series of iridium(III) complex-based chemosensors and biosensors have been constructed for the detection of a wide range of biologically important analytes, including ions, small molecules, amino acids, peptides and proteins. Chapter 1 provides an overview of the general synthetic routes and properties of iridium(III) complexes. General strategies for the development of iridium(III) complex-based chemosensors and the utilization of iridium(III) complex as a DNA probe in biosensors are also reviewed. Chapter 2 describes the application of an iridium(III) complex as a switch "on-off-on" chemosensor for the detection of both exogenously supplied and endogenously generated sulfide ion in vitro, in cellulo and in vivo. The optimized probe (1-Fe 3+), which coordinates Fe 3+ ion to an iridium(III) complex, could achieve a limit of detection (LOD) of sulfide ion down to 2.9 µM and establish a linear detection range from 10 to 1500 µM. While 1-Fe 3+ did not show any luminescence response in vitro under a high concentration of thiols, it exhibited a significant luminescence enhancement when the concentration of thiols was perturbed in cellulo and in vivo. This phenomenon can be explained by the presence of cystathionine gamma-lyase (CGL) and cystathionine beta synthase (CBS) in cellulo that could catalyze the conversion of the hydrogen sulfide (H 2 S) precursors, including cysteine and glutathione (GSH), into H 2 S. The results of this work have been published in a peer-reviewed scientific journal (Biosens. Bioelectron, 2017, 94, 575). Chapter 3 discusses the adaptation of an oligonucleotide-based Vascular endothelial growth factor 165 (VEGF 165) biosensor on a portable microfluidic device. An iridium(III) complex with an extensive conjugation system was used as a long- lived and red-emitting G-quadruplex probe. The polypropylene (PP)-based suspended-droplet microfluidic chip allows easy sample introduction, flexible sample volume range and valve-free manipulation of a stepwise reaction. We successfully assembled all the required components, including a ultraviolet (UV) lamp, a filter, a rotatable sample holder and a detector, into a portable box. The device could achieve a LOD of VEGF 165 down to the picomolar level, which is comparable to the results of a conventional fluorometer. The results of this work have been published in a peer-reviewed scientific journal (Dalton Trans., 2019, 48, 9824) The integration of graphene oxide nanomaterial to an oligonucleotide- based isothermal signal amplification system is presented in Chapter 4. Strand displacement amplification (SDA) could substantially amplify the signal from the target Hepatitis B virus (HBV) gene, while the electron accepting graphene oxide could effectively quench the emission of iridium(III) complex and enlarged the luminescence fold-enhancement of the system. The system could achieve a LOD for the HBV gene down to the picomolar level and was selective for the wild-type HBV gene over the single-base mutated HBV gene. The operation mechanism and the important rules for the formation of a stable split G-quadruple are detailed in this chapter. The results of this work have been submitted to a peer-reviewed scientific journal. In Chapter 5, the adaptation of SDA on an exonuclease III-assisted amplification (EXO) as a quadruple-cycle phosphorescence amplification system is reported. A systematic three-round structural optimization campaign was performed for the first time to iteratively improve the G-quadruplex selectivity of a large pool of iridium(III) complex. The proof-of-principle application of a self-assembly tetrahedron nanostructure (TNS)-based aptasensor was demonstrated using a cancer biomarker mucin 1 as the target analyte. This TNS-based aptasensor revealed a 57% higher luminescence enhancement compared to the conventional dsDNA aptasensing approach. The results of this work will be submitted to a peer-reviewed scientific journal upon completion of mechanism studies. Chapter 6 summarizes the properties, advantages, improvements and potentials for the developed iridium(III) complex-based sensors

Comments

Principal supervisor: Dr. Ma Edmond Dik Lung ; Thesis submitted to the Department of Chemistry

Bibliography

Includes bibliographical references (pages 173-181)

Available for download on Thursday, August 04, 2022



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